The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. However, these advances have increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component that can be created using a fabrication process) has decreased.
The constantly decreasing geometry size leads to challenges in fabricating high voltage semiconductor transistor devices. These high voltage (HV) transistor devices may need a sufficiently large voltage drop from a gate of the transistor device to a drain region of the transistor device. Traditionally, the large voltage drop has been accomplished by pushing the drain region away from the gate and source region, effectively lengthening the drift region between the gate and the drain. However, as transistor device sizes become smaller, it becomes impractical to lengthen the drift region. The drift region length affects various reliability characteristic such as hot carrier injection (HCI) and time dependent dielectric break down (TDDB). Hot carrier injection (HCI) is a phenomenon in solid-state electronic devices where an electron or a “hole” gains sufficient kinetic energy to overcome a potential barrier necessary to break an interface state. Since the charge carriers can become trapped in the gate dielectric of a metal-oxide semiconductor (MOS) transistor, the switching characteristics of the transistor can be permanently changed if the HCI is not sufficiently controlled. Time-dependent dielectric breakdown (TDDB) is a failure mechanism in MOS field effect transistors (MOSFETs), when the gate oxide breaks down because of formation of a conducting path through the gate oxide to substrate. This is due to an electron tunneling current, when MOSFETs are operated close to or beyond their specified operating voltages.
Therefore, while existing methods of fabricating high voltage transistors have been generally adequate for their intended purposes, they have not been entirely satisfactory in every aspect.